The instant invention pertains to semiconductor device fabrication and processing and more specifically to a method of fabricating a higher dielectric constant material using a silicate.
The trend in semiconductor device processing is to make the devices smaller so that more devices can be fabricated in a given area. This scale down affects substantially all of the device, so that each feature is scaled down. This is particularly problematic for the gate structure and capacitors, because capacitance is proportional to the dielectric constant of the material situated between the two plates of the capacitor and effective area of the dielectric material. In addition, the capacitance of a structure is inversely proportional to the distance between the two electrodes of the structure. Currently, since SiO2 is the material of choice for gate dielectrics, the thickness of this layer is decreased to compensate for the scaling down of the area of the capacitor. However, this thinning of the oxide layer is becoming problematic for a couple of reasons. First, as the thickness of the silicon dioxide layer is decreased to below about 3 nm, the leakage through the oxide becomes unacceptably high. In addition, the oxide layer ceases to act as an effective barrier with regards to keeping dopants which are implanted into the gate electrode to increase the conductivity of the gate electrode out of the channel regions. Second, extremely thin layers, unless they are formed from a process which is self-limiting, are very difficult to reproducibly fabricate. Third, any etching away of a thin layer, especially a gate insulator, using subsequent processing to etch other structures affects the thinner layer more dramatically than it would a thicker layer because a greater percentage of the thinner layer is removed than that of a thicker layer.
Another approach to solve this problem involves changing the gate insulating material to one with a higher dielectric constant. For example, BST, PZT, TiO2 and Ta2O5 are being considered for the next generation of gate dielectrics. However, each of these materials pose problems because the processing required to make these materials into effective gate dielectric materials conflicts with the processing of standard transistor structures. More specifically, each of these materials require a high temperature anneal in an oxygen-containing ambient, and this anneal can greatly degrade the underlying substrate and any other exposed oxidizable structures.
Hence a new material needs to be used which is relatively easy to process using standard gate structure processing techniques and which has a dielectric constant higher than that of silicon dioxide (xcex5≈3.9).
Basically, the instant invention involves a gate structure which includes an oxide or a silicate layer as the gate dielectric and a method for fabricating such a structure. More specifically, the gate insulator of the instant invention is preferably comprised of ZrO2, ZrSiO4, HfO2, or HfSiO4. Preferably, this layer has a dielectric constant of around 10 to 40 (more preferably around 15 to 30). In alternative embodiments, the dielectric layer of the instant invention can be utilized as a capacitor dielectric.
An embodiment of the instant invention is a method of forming a semiconductor device situated over a semiconductor substrate, the method comprising the steps of: forming a layer of suboxide material over the substrate, the suboxide material comprised of a material selected from the group consisting of: HfSiOx, ZrSiOx, LaSiOx, YSiOx, ScSiOx, and CeSiOx; and forming a structure on the layer of suboxide material. In an alternative embodiment, semiconductor device is a transistor where and the structure formed on the layer of suboxide material is a gate electrode (preferably comprised of: polycrystalline silicon, tungsten, titanium, tungsten nitride, titanium nitride, platinum, aluminum, and any combination thereof). In another alternative embodiment, the semiconductor device is a storage device where a bottom electrode is formed under and abutting the suboxide material which forms the dielectric to the storage device and the structure formed on the layer of suboxide material is the top electrode of the storage device.
The method of the instant invention may also include the step of: subjecting the semiconductor device to an elevated temperature in an ambient which contains oxygen after the step of forming a layer of suboxide material over the substrate and prior to the step of forming a structure on the layer of suboxide material. Preferably, the elevated temperature is around 400 to 600xc2x0 C. Alternatively, the method of the instant invention may include the step of: subjecting the semiconductor device to an elevated temperature in an ambient which contains ozone after the step of forming a layer of suboxide material over the substrate and prior to the step of forming a structure on the layer of suboxide material. Preferably, the elevated temperature is around 25 to 400xc2x0 C. In yet another alternative embodiment, the method of the instant invention may include the step of: subjecting the semiconductor device to an elevated temperature in an ambient which contains nitrogen after the step of forming a layer of suboxide material over the substrate and prior to the step of forming a structure on the layer of suboxide material. Preferably, the elevated temperature is around 500 to 600xc2x0 C.
Another embodiment of the instant invention is a method of fabricating an insulating layer situated between a conductive gate structure and a semiconductor substrate, the method comprising the steps of: forming a layer of HfSiOx on the semiconductor substrate; subjecting the layer of HfSiOx to an elevated temperature in an ambient comprised of a gas consisting of: O2, O3, N2, and any combination thereof; and forming the conductive gate structure on the layer of HfSiOx. The step of subjecting the layer of HfSiOx to an elevated temperature in an ambient comprised of either O2 or O3 may result in the increased oxygen content of the HfSiOx layer. Preferably, the layer of HfSiOx is formed by PVD, CVD, or e-beam evaporation using one or more solid targets.
Another embodiment of the instant invention is a method of fabricating an insulating layer situated between a conductive gate structure and a semiconductor substrate, the method comprising the steps of: forming a layer of ZrSiOx on the semiconductor substrate; subjecting the layer of ZrSiOx to an elevated temperature in an ambient comprised of a gas consisting of: O2, O3, N2, and any combination thereof; and forming the conductive gate structure on the layer of ZrSiOx. The layer of ZrSiOx to an elevated temperature in an ambient comprised of either O2 or O3 may result in the increased oxygen content of the ZrSiOx layer. Preferably, the layer of ZrSiOx is formed by PVD, CVD, or e-beam evaporation using one or more solid targets.